docs: bring the README, data sources and known issues up to date (#712)

Reflect the weather stack, analyst records and feed provenance, satellite pass predictions and live camera video that landed since the last full pass.

Co-authored-by: Matt Van Horn <[email protected]>

docs/KNOWN-ISSUES.md

@@ -1,6 +1,6 @@
 # KNOWN ISSUES
 
-Updated: July 8, 2026
+Updated: September 22, 2026
 
 This file tracks active runtime issues only.
 
@@ -78,6 +78,56 @@ Status: Open (owner-accepted 2026-07-08, documented)
 
 ---
 
+### Weather layers: coverage and meaning
+Status: Open (source limits, by design)
+
+- **Rain radar covers the contiguous United States only.** It shows MRMS
+  reflectivity in dBZ, not rainfall rate or a forecast; a gap in coverage does not
+  mean no precipitation.
+- **Lightning density is a ground-network grid, not GLM flashes.** It is NOAA's
+  15-minute density product derived from Vaisala NLDN/GLD360 on an approximately
+  8 km grid, for the Americas and Pacific only (110°E across the dateline to 0°,
+  25°S–80°N). It is not a live strike counter or an all-clear.
+- **Cyclone advisories cover NOAA's basins only:** the Atlantic and the
+  eastern/central North Pacific (NHC and CPHC). Storms elsewhere do not appear.
+  The cone is forecast-center uncertainty, not storm size.
+- **Satellite clouds:** global infrared is hourly with typically 2–3 hours of
+  source latency. Clouds only is a brightness filter, not a cloud mask.
+- **Wind is a forecast.** The animation flows through one forecast on an
+  approximately 1° grid and does not advance forecast time or follow the
+  observed-history timeline.
+- **History is not shared.** Share links carry the weather layers and their
+  settings but open at Latest.
+- **3D Tiles detail window during history playback:** when a frame's detail image
+  is slow to arrive, the window may fall back to the coarser full-extent image
+  until it does.
+- Native hardware GPU behavior of the wind and weather renderers is not yet
+  verified.
+
+---
+
+### Satellite passes and analyst answers
+Status: Open (by design)
+
+- Pass predictions search the next 24 hours for satellites in the loaded catalog.
+  Visibility is a geometric estimate (satellite sunlit, observer's Sun at or
+  below −6°); it ignores weather, satellite brightness and orbital-element age.
+- Analyst counts and ranks cover a bounded set of loaded records (by default
+  2,000 per layer for satellites, datacenters and dams), so omitted records can
+  change a nearest or count answer. Satellite distance is ground distance.
+
+---
+
+### Live camera video (HLS)
+Status: Open (limits)
+
+- At most two live-video sessions run at once. RTMP-only sources and encrypted,
+  fMP4 or byte-range playlists are not supported.
+- When live video fails, the camera falls back to its labeled still, Street View
+  or placeholder frame, which is not live video.
+
+---
+
 ## Closed / Intentional (for clarity)
 
 ### Proxy SSRF and error-surface hardening gaps
@@ -118,5 +168,14 @@ Context:
   converted to **live NASA FIRMS data** on 2026-07-16: the `/api/firms` proxy merges
   three VIIRS NRT sources (trailing 24 h, 30 min cache, serve-stale-on-failure) and the
   bundled snapshot was deleted. Requires a free server-side `FIRMS_MAP_KEY`; without it
-  the layer shows a KEY REQUIRED state.
-- Weather radar is still held out of OSS v1 after QA found the previous overlay did not provide reliable visible value.
+  the layer row reads "Needs FIRMS_MAP_KEY — add it in Provider Settings".
+
+---
+
+### Weather radar held out of the open-source release
+Status: Closed — observed rain radar shipped (September 2026)
+
+Context:
+- Rain radar, Satellite clouds, Lightning density, Wind and Cyclone advisories
+  are in the Weather group of Data Layers. Their current limits are listed under
+  "Weather layers: coverage and meaning" above.